@SnapCrackleandStop re your more recent long post, it isn't that I am not "getting it" as you have said a few times, it is that I don't agree with you. Our mindsets are different.
Basic rules of grammar ie what is taught at school level have been around a long time and haven't changed much, and like maths, things become more interesting the more advanced you get, but in relation to what should be learned at school, it is pretty fixed and basic. Until the 1950s/60s (later in some regions) the same rules were taught to the whole country without eroding local dialects. Grammar has not substantively changed since then. I went to uni with people from other areas of the UK who could write and speak using grammar correctly but would chat away in local dialects in the pub. The two things are different.
I think that your theories about how to teach children would be very limiting for children. The language someone has available to them affects how they think - teaching complex language facilitates complex thought - it isn't possible to understand complex language without being aware of the rules and variances due to context which govern it. A knowledge of correct complex language facilitates communication and understanding, on an interpersonal level and on the international stage. English people with a good knowledge of English grammar find it much easier to learn foreign languages, compared with those who don't. "Would of" does not translate, whereas "would have" does - in pretty much every language.
Absolutely realistic to have a reliable source created.
If there were more than one way of looking at any particular point, both could be explained in the reliable source - the example which springs to mind is the use of shall vs will in relation to which the old rules are still correct and the use of the two words interchangeably is also seen as correct.
Your conundrums about sentences and the others set above - these are interesting but are not at relevant to what I am talking about. In relation to basic formal grammar the meaning of "sentence" is reasonably straightforward, and looking at the definition in a dictionary is a good start (ie in relation to teaching basic formal grammar).
Neither you nor I are necessarily right or wrong from the point of view of linguists or philosophy, or other areas of theoretical study, but I think you are wrong from the point of view of teaching children and giving everyone reliable accurate sources.